Multifocal atrial tachycardia is a rapid heart rate that occurs when too many signals (electrical impulses) are sent from the upper heart to the lower heart.

Causes, incidence, and risk factors:

The human heart gives off electrical impulses, or signals, which tell it to beat. Normally, these signals begin in an area of the upper right chamber called the sinoatrial node (sinus node or SA node). This node is considered the heart's "natural pacemaker." It helps control the heartbeat. When the heart detects a signal, it contracts (or beats). The normal heart rate in adults about 60 to 100 beats per minute. The normal heart rate is faster in children.

In multifocal atrial tachycardia (MAT), multiple locations within the heart fire signals at the same time. Too many signals lead to a rapid heart rate -- anywhere from 100 to 250 beats per minute. The rapid heart rate causes the heart to work too hard. If the heartbeat is very fast, the heart has less time to fill up with blood, so it doesn't have the right amount of blood to pump to the brain and the rest of the body.

MAT is most common in people age 50 and over. It is often seen in people with conditions that lower the amount of oxygen in the blood. These conditions include: